1. Field of the Invention:
This invention relates to an apparatus for measuring the size of a seamed portion of a can, e.g., a three-piece can or a D & I can, constituted by seaming edges of a can end and a can body.
2. Description of the Prior Art:
After a can which is either small or large in size has been filled, an edge of the opening of the can body is sealed with a can end. The maintenance of the size of the seamed portion of the can is a factor for determining the seal property of the can, and it is one important control item for maintaining the quality of the can contents.
The sectional views of FIGS. 6 and 7 illustrate a process of seaming and a resulting seamed portion. As shown in FIG. 6, a curled portion 2a of a can end 2 is curled into the inside of a flange portion 1a of a can body 1 by a first seaming roll. Then, as shown in FIG. 7, the portions 1a and 2a are tightly pressed together by a second seaming roll to obtain a seamed portion 3. The seamed portion 3 is formed such that it is inclined outwardly from an extension X--X of the can body 1 by a small angle .theta. (about 4 degrees) for the removal of the processing tool. Further, an upwardly open, shallow dish-like countersink 4 is formed on the inner side of the seamed portion 3.
For inspecting the quality of the seal of the seamed portion 3, tests are conducted from many aspects. More specifically, the thickness T and width W of the seamed portion 3 and the depth C of the countersink, as shown in FIG. 8, are measured. Further, the can height H (not shown) is measured. These measurements are performed for the following reasons. The thickness T of the seamed portion is increased if the pressure applied in the press operation is insufficient. If the pressure applied is excessive, on the other hand, a crack is generated in the seamed portion 3, so that the thickness is reduced. In either case, the seal is imperfect. As for the width W of the seamed portion, it is reduced if the pressure applied in the press operation is insufficient. If the curled portion 2a as shown in FIG. 7 is insufficiently curled, on the other hand, the width of the seamed portion is increased. In either case, the seal is imperfect. As for the depth C of the countersink, like the width of the seamed portion, it is increased if the curl of the curled portion 2a is insufficient, while it is reduced if the curl is excessive. In either case, the seal is imperfect. As for the can height H, its variations affect T, W and C, so that it also constitutes an item to be checked.
The thickness T and width W of the seamed portion, the depth C of the countersink and the can height H are checked for the reasons noted above, and cans for which these values exceed certain predetermined values, particularly the values of T and W, are rejected.
Apparatus for measuring the values noted above include an apparatus for measuring th width of a seamed portion as disclosed in Japanese Patent Laid-Open Publication No. 165501/1980, an apparatus for measuring the thickness of a seamed portion as disclosed in Japanese Patent Laid-Open Publication No. 203805/1985 and an apparatus for measuring the countersink depth of a can end as disclosed in Japanese Patent Laid-Open Publication No. 247111/1985.
A summary of the construction and function of these apparatuses will be described in reference to FIGS. 9 to 11.
FIG. 9 is an elevational view showing the apparatus for measuring the width of a seamed portion as disclosed in Japanese Patent Laid-Open Publication No. 165501/1985. This apparatus uses a micrometer 70 provided with a frame 71 and a spindle 72, which clamp a seamed portion during measurement. The spindle 72 of the micrometer 70 is vertically moved by an air cylinder 73. The whole micrometer 70 is downwardly moved by an air cylinder 74 while it is upwardly moved by a spring 82. Further, the micrometer 70 and air cylinder 74 are moved horizontally outwardly (i.e., in the direction of arrow Y) by an air cylinder 75, while they are moved toward the can (i.e., in the direction of arrow Z) by a spring 83. Since the apparatus has the structure as described above, by setting a can 5 to be measured on a clamp base and releasing the operation of the air cylinder 75, the frame 71 of the micrometer 70 is moved horizontally by the spring 83 to be brought into contact with the can body below the seamed portion of the can 5. Then, by stopping the operation of the air cylinder 74, the frame 71 is moved upwardly by the spring 82 to be brought into contact with the lower end of the seamed portion of the can 5. Subsequently, the spindle 72 is lowered by operating the air cylinder 73 to clamp the seamed portion between the frame 71 and the spindle 72 for measuring the width of the seamed portion. Defects that are involved with this apparatus will be described later. FIG. 10 is an elevational view showing the apparatus for measuring the thickness of a seamed portion as disclosed in Japanese Patent Laid-Open Publication No. 203805/1985. This apparatus again uses a micrometer 70 provided with a frame 71 and a spindle 72, which clamp a portion being measured. The spindle 72 is moved laterally by an air cylinder 76. The whole micrometer 70 is tiltably suspended by a shaft 79, so that the frame 71 and spindle 72 can be tilted in accordance with the small angle .theta. of the seamed portion noted above. The whole micrometer 70 may also be moved horizontally toward the can 5 by an air cylinder 77 and outwardly by a spring 84. The micrometer 70 and air cylinder 77 are further moved vertically by an air cylinder 78. With the apparatus of this construction, the can 5 being measured is set on a clamp base, and the air cylinder 78 is operated to lower the frame 71 of the micrometer 70 to a position close to the can end as shown in FIG. 10. Then, by stopping the operation of the air cylinder 77, the micrometer 70 is moved horizontally by the spring 84 to bring the frame 71 into contact with the inner side of the seamed portion. At this moment, the whole micrometer 70 is tilted by the shaft 79. Subsequently, the air cylinder 76 is operated to move the spindle 72 laterally to clamp the seamed portion between the frame 71 and the spindle 72 for measuring the thickness of the seamed portion. Defects that are involved with this apparatus will be described later.
FIG. 11 is an elevational view showing the apparatus for measuring the countersink depth as disclosed in Japanese Patent Laid-Open Publication No. 247111/1985. This apparatus uses a micrometer 70, which is provided with a frame 71 to be held in contact with the top of the seamed portion and a vertically movable spindle 72. The whole micrometer 70 is vertically moved by an air cylinder 80. The whole micrometer 70 and air cylinder 80 may be moved horizontally toward the can 5 by an air cylinder 81 and outwardly by a spring 85. With the apparatus of this construction, the can 5 to be measured is secured to a clamp base, and then the air cylinder 81 is operated to bring the whole micrometer 70 to a position above the can. Then, the air cylinder 80 is operated to bring the frame 71 into contact with the top of the seamed portion and bring the spindle 72 into contact with the outer surface of the can end. Subsequently, by releasing the operation of the air cylinder 81, the whole micrometer 70 is moved horizontally outwardly (i.e., in the direction of arrow S) by the spring 85, and the spindle 72 is slid into the deepest part of the countersink, whereby the countersink depth is measured. Defects that are involved with this apparatus will be described later.
Several apparatuses are well known and used as an apparatus for measuring the can height. They are not described in detail here, but an apparatus as shown in FIG. 5 will be described as an example. The apparatus has a beam 37, which extends from the upper end of a support 36 extending upright from a base, on which the can to be measured is placed. An air cylinder 38 and magnetic scale 39 are secured to the beam 37 such that they extend vertically. A can height measurement member 18 is mounted on the lower end of the scale 39 such that it is in contact with the end of a rod 40 of the cylinder 38. When the rod 40 is moved vertically with the operation of the cylinder 38, the measurement member 18 is also moved vertically. A cable 27 of the scale 39 is connected to the measurement unit, and the measured can height is transmitted to the unit.
The apparatuses described above, particularly those disclosed in the three publications noted above, are excellent apparatuses, provided with spring mechanisms for bringing the micrometer into contact with a portion under measurement slowly without causing damage to the can. In these apparatuses, however, defects are encountered in that measurements of individuals items of data performed in seperate steps.
Recently, cans and canned goods have been manufactured at a production rate as high as 400 to 500 cans per minute. Therefore it is necessary to check the thickness and width of the seamed portion frequently, and to eleminate the cause of a defect as soon as the defect is found. To determine the cause, it is necessary to know the values of the thickness and width of the seamed portion of the can under measurement at the same point of the seam. To eliminate the cause, changes in the counterdepth and/or can height are considered due to changes in the size of the seamed portion.
With the prior art measurement apparatus, however, a measurement of only a single item can be performed with one apparatus. This means that the can being measured has to be moved for each measurement; for instance, after measurement of the thickness T of the seamed portion with a seamed portion thickness measurement apparatus, in order to measure the width W, the can has to be moved to the station where there is a seamed portion width measurement apparatus. Therefore, the overall measurements require a great deal of manhours. Further, since the prior art measurement apparatus each permits measurement of only a single item, it is impossible to obtain measurement data about the same point of the seamed portion for the individual measurement items, that is, it is impossible to obtain data of the thickness, width, etc. with respect to the same part of the seamed portion. Therefore, when determining the cause of a defect, the correlation of the individual measurement items is inevitably looked at by examining the correlation of average values obtained for each measurement item. If it is possible to obtain data for each item with respect to the same part of the seamed portion, it is effective to compare each item data to detect items of increased values and items of reduced values. However, correlation can not be obtained among data obtained for different parts of the seamed portion because of waving, eccentricity, inclination, etc. of the seamed portion. Hence, it is usual to check the increasing and reducing tendencies of average value data and to check the correlation of these data. However, it is time-consuming to obtain average values, and the correlation based on the average values is inaccurate, thus frequently resulting in the incomplete elimination of the cause of a defect.
If it is possible to obtain data as noted above, particularly at least width and thickness data, with respect to the same part of the seamed portion of the can and simultaneously, it would greatly contribute to the can quality control. No apparatus which can meet such criteria has heretofore been provided.
With the prior art apparatuses for measuring the thickness, width, etc. of the seamed portion, measurements are performed separately with respect to some parts of the seamed portion of the can, so that data with respect to the same part can not be obtained even if those apparatus are combined.